Okay I have no clue what kind of room this would leave to play with, but the first thing to start off with is the port whole itself that ill cut in through the cab. The biggest I could possibly go is (10 tall x 52 wide x 6 thick). As far as the box itself in the bed. Max is (17 tall x 60 wide x 21 front to back). Would rather build to the tallest and widest so I can still get my dirtbike in my truck with the tailgate down. Im goin to upload a pic I drew up of actual sizes of the bed to maybe see if the box was to have to go past 21inches (btw im no artist). Would rather build 6th order and kerf port the inside box. Anyone willing to help would be my life saver and I appreciate each and everyone of your oppinions. Thank you!